This invention relates to radar processing apparatus and methods and, more particularly, to such apparatus and methods for processing signals including radar return (i.e., primary target) signals and beacon reply signals from, for example, aircraft on the ground or in the air.
Radar systems for detecting moving targets have been used in a variety of applications including the control of airport traffic. Systems to control aircraft traffic on an airport surface and in the air above the airport are in use in airports across the United States and elsewhere. These systems provide positional information to help direct aircraft and thus prevent them from colliding with each other and with other non-aircraft objects such as luggage-carrying vehicles traveling on the airport surface.
One radar system currently being used to control airport traffic in airports in the United States is known as the Airport Surveillance Radar-9 (ASR-9). The ASR-9 was developed and tested in the 1970s and 1980s, and it was deployed sometime around 1990. When used in airports in urban locations, the performance of the ASR-9 typically degrades due to, for example, the reflection (i.e., multipath or multipathing) of beacon signals and radar return (i.e., primary target) signals, ground traffic breakthrough, and the ASR-9's limited azimuth resolution of closely spaced targets. In areas where large numbers of aircraft are operating, beacon reply signals are often overlapped or "garbled", further degrading the ASR-9's performance and effectiveness.
Briefly and in general, when a radar beam or radar pulse (transmitted by, for example, an airport traffic control radar system such as the ASR-9) is incident upon an aircraft in the air, one or more beacon reply signals are emitted by a transponder in the aircraft. The beacon signals contain identifying information about the aircraft such as aircraft type, flight number, aircraft number, and aircraft altitude. In addition to the positional information provided by airport radar systems, the identifying information contained in the beacon signals can be displayed to an air traffic controller to provide the controller with a more complete picture of the airport traffic.
In general, the ASR-9 is not capable of compensating for the problems encountered when it is used in urban airport settings. More specifically, an Array Signal Processor (ASP) within the ASR-9 generally lacks the memory and processing power necessary to execute advanced signal processing techniques which have the potential to compensate for one or more of the problems encountered when operating the ASR-9 in an urban setting.
It is desired to eliminate or mitigate the performance problems of an ASR-9 operating in an urban airport setting. It also is desired to minimize the cost of addressing these performance concerns.